Thermionic-valve system



Imm mi@ W5@ M. K. TAYLOR mm.. 4959949 THERMIoNlc-VALVE SYSTEM Filed July 22, 1947 2 Sheets-Sheet 2 INVENTOR. MAURICE K.TAYLOR FREDERIC C. WILLI AMS ATTO RNEY Patented Jan. 31, 1950 UNITED STATES ATNT FFICE THERMIONIC VALVE SYSTEM Section 1, Public Law 690, August 8. 1946 Patent expires November 5, 1965 (Cl. Z50-36) 12 Claims.

'Ihis invention relates to thermionic-valve systems. More particularly the invention relates to improvements in thermionic-valve oscillatory systems of the type disclosed and claimed in the copending application of Maurice K. Taylor et al., Serial No. 766,392, filed August 5, 1947, entitled Control arrangement for thermionic valve systems, andl assigned to the same assignee as the present applicatiom wherein it is possible to pro- Vide either for the4 cyclic operation of each of such systems singly in, predetermined order or for the substantially uninterrupted operation of only a specific one of them.

The expression substantially uninterrupted Operation, used above and hereinafter is intended to mean that the specic system operates continuously except for a short interruption at the end of each operating cycle of the control arrangement.

In the specication of the above-identified cpending `patent application, there is described a thermionic-valve system comprising two signalmodifying means together with a switching system which either allows the two means to operate alternately or allows only a specic one of them to operate. Operation or nonoperation of a signal-modifying means is determined by the connection or disconnection of the high-tension supply to the receiving and transmitting valves included in the signal-modifying means.

Certain diinculties arise during the period of change-over from one signal-modifying means to another,` that is to say, when the high-tension supply is disconnected yfrom one means and connected to the other.

The rst diiculty arises from the fact that the receiving valve and transmitting valve o each means are each provided with an automatic gridbiasing arrangement comprising -a resistance in parallel` with a condenser in the cathode` lead. Consequently when, after such a means has been operating, the high-tension supply to it is disconnected due to movement of the switch, the condenser forming part of the grid-biasing means discharges and the potential or the cathode of the valve becomes nearly equal to earth potential. When the high-tension supply to, this means is switched on again after a period during which the other signal-modifying means has `been operating` the negative bias potential applied to the receiving valve and the transmitting valve in the rst-mentioned means is small since their cathodes are nearly at earth potential, and it is usually so.` small as to allow sel-oscillationv in each control-grid cathode circuit to occur, thereby causing unwanted transmission. This state of aiairs continues until the cathode potentials rise to their operating values.

A second difculty arises because a connection is made to the control grid of the transmitting valve in each means from the anode of an amplifier valve which is common to both means. When a signal pulse is received by an operating signalmodifying means, the potential of the anode of the common amplifier valve rises. Hence not only does the potential of the control grid of the transmitting valve in the operating means rise positively, but so does the potential of the control grid of the transmitting valve in the non-operating means. In the case of this latter valve, its anode potential is zero, its control-grid potential is positive and its cathode potential is nearlythat of earth. Consequently, the control grid and cathode of this transmitting valve may operate as a diode valve, the control grid taking current. It will be seen that a transmitting Valve in a nonoperating means may thus add an extra load t0 the common amplifier valve, thereby reducing the driving power applied to the transmitting valve in the operating means. This would cause a reduction in the amplitude of thepulse transmitted from the operating means. Furthermore the width of the pulse may be affected since the current through the pulse-widening circuit will.' then include a component due to grid current in the transmitting valve in the nonoperating means.

It is an object of the present invention, therefore, to provide a new and improved thermionicvalve system which avoids one or more of the above-mentioned disadvantages and limitations of prior such systems.

It is another object of the invention to provide a new and improved thermionic-valve system which includes therein an arrangement for selectably controlling the operation of each of a plurality of thermionic-valve systems which constitute said first-mentioned system.

In accordance with a particular formA of the invention, a thermionic-valve system comprises a plurality of selectafbly Operated thermionic-valve oscillatory systems each includingl at least one oscillator valve having an input circuit therefor and a self-bias means in each ofthe input circuits ior developing a self-bias potential for the oscillator valve associated therewith when the oscillatory system including the. aforesaid associated oscillator valve is selectably operated. The thermionicfvalve systemA also, includes a control systemior applying, when any selected oneof the oscillatory systems is operating, a control potential to the self-bias means of the oscillator in each nonoperating oscillatory system to prevent self-oscillation immediately upon selection of a nonoperating oscillatory system for ope-ration. The system further includes means, responsive to the selection of the last-mentioned system for operation, for removing the control potential from the self-bias means of the oscillator valve thereof.

In order that the invention may be more readily understood it will now be described, by way of example and with reference to the accompanying drawings, with relation to its application to the control of two thermionic-valve responder systems in an aircraft for providing identification of the latter in conjunction with the pulsed exploring waves of two different types of radio-location apparatus. It is to be understood however that the invention is by no means limited to such an application or to the control of two thermionicvalve systems only.

In the accompanying drawings, Fig. l is a schematic representation of one form of responder means for receiving and retransmitting signal pulses transmitted from one e. g. ground, radiolocation station; Fig. 2 represents schematically two responder means, embodying a control arrangement for receiving and retransmitting signal pulses transmitted from each of two types of ground radio-location station; Fig. 3 is a schematic diagram of a control arrangement adapted for use in connection with the two responder means represented in Fig. 2; and Fig. 4 is a schematic diagram of a control arrangement in accordance with an embodiment of the invention.

In the usual method of effecting the radiolocation of aircraft, a pulsed exploring wave comprising a series of signal pulses, each pulse being formed by a short burst of radio-frequency energy, is transmitted from one or more ground stations. Such pulses, if incident upon an aircraft, are reected therefrom and part of this reflected energy may be received by the ground station and applied to apparatus for giving an indication of the presence of the aircraft.

Such a reflected signal, however, does not give an indication of the nature of the aircraft. Thus in wartime it is impossible to state from such lreceived signals whether the aircraft is f friendly or enemy origin.

In order to provide an indication of the nature of the aircraft, all aircraft of friendly origin may be fitted with a signal receiving and retransmitting means usually known as a responder. Such a responder may comprise the apparatus shown in the block diagram of Fig. 1 of the accompanying drawings. The signal pulses transmitted from the ground station are received by an aerial 40 and applied to a wave-signal selector or tuned circuita, the tuning condenser of which sweeps through a band of frequencies including the carrler frequency of the pulsed exploring wave. When the circuit a. is tuned to the carrier frequency of one particular ground station, each received pulse is amplified by a super-regenerative receiving circuit b, supplied with a quenching oscillation from an oscillator c. The output from stage b is applied to a detector circuit d and the rectied output therefrom is applied to a pulseamplier stage e. The amplied output is fed to a pulse-widening or shaping circuit f, which includes a capacitance the value of which may be varied automatically by suitable driving mechanism. and thence to the control grid of a transmitting valve included in a modulated wave-signal transmitter lc. The transmitting valve may be the same valve as that in the superregenerative stage b, or it may be a separate valve having the same tuned circuit a connected between its anode and control grid; that is to say, the tuned circuit a may be common to both the receiving valve and the transmitting valve. However, for the sake of simplicity, Fig. 1 of the drawings indicates a transmitter which is complete in itself. The arrangement of Fig. l does not embrace the present invention and all of its several components may have a construction and operation well understood by those skilled in the art, rendering a further detailed description thereof unnecessary.

By the provision of such apparatus a signal pulse received from a ground station, is translated n the usual Way by superregenerator a, detected in detector d, amplified and shaped in units e and f, respectively, and applied as a modulating signal to transmitter 1c. Thus, a received pulse is retransmitted in amplied form and with considerably increased width, the increase in width being determined by the pulse-widening circuit f. This amplified and widened retransmitted pulse appears as such when rendered visible on the screen of a cathode-ray oscillograph incorporated in the apparatus at the ground receivingr station. Therefore, it is possible to distinguish between an aircraft tted with the above-described. responder means and an aircraft which is not so fitted by observing either the width or the height or both of the reply pulse signal received at the ground station.

Two classes of ground-station radio location are in general use, the carrier frequency of the pulses from each class being in a different frequency band. One class, which comprises earlywarning stations, is employed for the purpose of giving a long-range indication of the approach of an aircraft. The other class is for short-range detection and, when provided in association with anti-aircraft batteries, is employed as a -gunlaying station for the purpose of indicating the bearing and range of an aircraft. Since it is only necessary to know the bearing and range of an enemy aircraft just before the moment of ring, the effective area of this latter class of ground stations need only be small. Because the carrier frequencies of the signals from the two classes of ground station may be widely separated and, on account of their high value, it would appear necessary to provide an aircraft with two complete and independent sets of responder apparatus in order that appropriate identification signals may be returned to both classes of ground stations by a friendly aircraft. Where that is done, the frequency band of one responder includes only the carrier frequencies of the pulses transmitted from the early-warning stations and the frequency band of the other responder includes only the carrier frequencies of the pulses transmitted from the gun-laying stations. Such an arrangement has, however, several disadvantages. The apparatus is, of necessity, unduly large because only the supply unit is usually common to both responder circuits. Since the power supply has to be larger than that of a single responder, the supply unit itself is both heavier and more costly. A further technical difculty arises because of mutual interference between the two aerial systems associated with the two responder circuits.

Since the aircraft ls likely to be in an earlywarning area for the greater part of its time,

it is sufficient in many installations' lf'the'responder apparatus of` such aircraft is rendered responsive to early-warning stations for most of the time and if automatic switching means are provided to permit response to gun-laying stations for, say, two seconds in every six seconds, thus enabling thel aircrafts presence to be made known should it enter a gun-laying area. Itis essential, however, in order to avoid serious mistakes, that if the apparatus happens to 'be responsive to gun-laying stations upon entering a gun-laying area itis not then switched over so as to respond to signals from early-warning stations; or if it happens to be responsive to earlywarning stations it will not,-after the subsequent switching to respond to gun-laying stations, switch back again to respond to early-warning stations until the aircraft leaves the gun-laying area. That is to say, while the aircraft is within a gun-laying area, it should respond only to signals from gun-laying stations.

In Figs. 2 and 3 of the accompanying drawings two responder means of the type represented in Fig. 1 are embodied in an aircraft and associated with an improved control arrangement. The responders have certain of their components common to one another. Referring more particularly to Fig. 2, one responder means :c is adapted to respond only to signal pulses transmitted from short range or gun-laying stations. The other responder means y is adapted to respond only to signal pulses transmitted from early-warning stations. Each circuit is similar to that of Fig. 1, the components peculiar to means .r and y bearing the same reference letters as the corresponding components in Fig. 1 with either a prime or double-prime notation respectively. The quench-frequency oscillator c and the pulse amplifier e are common to both responders.

The output from the amplifier stage e, besides being taken to the pulse-widening or shaping circuits f and f", each of which includes a capacitance whose value may be varied automatically by a suitable driving mechanism, is arranged to be fed also to a diode rectifier :g and then to a D. C. amplifier h. The amplied output from amplifier h is adapted to energize a control arrangement or switching system z' arranged to causeoperation of either superregenerative stage b or superregenerative stage b, and of either the driving mechanism included in pulse-widening circuit f' or the driving mechanism included in pulse-widening circuit f.

The switching system z', see more particularly Fig. 3, comprises a change-over switching means, having one operating condition which permits the responders to operate singly in a predetermined cyclic order and having another operating condition which permits the substantially uninterrupted operation of only a specific responder, namely, that designated While this switching means may be provided by tube elements having oif and on operating conditions, simplicity may be obtained from the use of a two-position, multi-sectional mechanical switch as illustrated. This switch is formed by five double-breaksinglepole switch sections I, 2, 3, l and 5. One contact I of the double-'break single-pole switch element I is connected to the positive terminal of a high-tensionl supply, which supply is also'oonnected to a spring blade 'l arranged to be cyclically actuated by a continuously rotating cam 8. The other contact l bof switch element I is connected to a contact 9 associated with .spring'blade l andalso to the anode of "the receiving valve in the stage 12' by way of the tuned circuit a'. Thecontact 2a is connected to contact I0 associated with spring blade 1, and contact 2b is joined to the anode of the receiving valve in stage b" Vby way of tuned circuit a". Contact 3a of double-break single-pole switch element 3 is connected to contact IIa of anotherspring blade Il, `which is arranged to be operated by a cam 8' mounted rigidly on the same spindle as cam 8, contact Hb coacting with contact IIB being joined by way of a hold-on coil I2 to one terminal of a suitable, e. g. liz-volts, D. C. supply E. The other contact 3h of switch element 3 is connected to the other terminal of the 12-volts supply E. Contact It of double-break single-pole switch element 4 is joined directly to contact 5B of double-break single-pole switch element 5 and is also connected to the first-mentioned terminal of the 12volts supply E. Contact 5b of switch element 5 is connected to the driving mechanism associated with pulse-widening circuit f and contact tb is connected to the driving mechanism associated with the pulse-widening circuit f. `A contact I3, associated with spring blade 1, is connected by way of an energizing coil I4 to the anode of the valve forming the D. C. amplifier h. Contact dband contact 5b are joined together by way of the series connection of two 12-vo1t lamps l5, I6, the point common to the lamps being joined to contact 3b and hence to the secondmentioned terminal of the 12 volts supply E.

Cam 8 is designed in such a manner that, during a complete period of its rotation, spring blade 'l' makes contact with contact I il for fourteen seconds and subsequently makes simultaneous contact with contacts 9 and I3 for two seconds. Cam 8a is arranged to engage with a blister on spring blade I I one second before spring blade l makes contact with contacts 9 and i3, the period of engagement being about one-half of a second. The cams are arranged to be driven continuously in an anti-clockwise direction.

It is arranged that a negative bias potential is applied to the control grid of the valve in the D. C..amplifier h of sufficient amount to prevent conduction. Its precise value is such that the D. C. potential across the diode rectifier g' which would be developed as a result of the rectication of signal pulses received from early-warning stations and which is dependent upon the repetition frequency of the exploring wave pulses, is not sufficient to overcome this negative bias potential, whereas that due to rectification of signal pulses received from gun-laying stations, which pulses have a higher repetition frequency, is sufficient to overcome this bias potential.

In operation, when coils llt and I2 are deenergized, the change-over switch is biased, e. g. by spring means Il, to a rst position such that double-break single-pole switch sections I, 3 and 4 are open and the double-break single-pole switch sections 2 and 5 are closed as shown. Assuming cam 8 to be in such an angular position as to cause spring blade l to make contact with Contact I, the high-tension supply is con'- nected to the anode of the receiving valve in stage b" `which is adapted to receive only signals transmitted from early-warning stations. Siglnals from these stations are received and the retransmitted signals are appropriately widened since a driving potential is applied to the driving mechanism associated with pulse-widening means j" from the I2 volts supply E by way of .doublebreak single-.pole switch element 5.

One second before spring blade 1 makes contact with contacts 9 and I3, contact between IIa and Ilb is broken by virtue of the engagement of cam Ba with the blister on spring blade II. No current is flowing through the hold-on coil I2 at this moment since double-break single-pole switch element 3 is open and hence the opening of contacts I'Ia and I Ib has no eiect upon the circuits. The opening of contacts I la and I ib exists for about one-half of a second and after a further period of one-half of a second, spring blade 'i breaks contact with contact I and makes contact with contacts 9 and I3. The high-tension supply is now disconnected from the anode of receiving valve in stage b and is connected to the anode of receiving valve in stage E which is adapted to receive only signals transmitted from gun-laying stations. The high-tension supply is also applied to the anode of the valve in the D. C. amplier h by way of energizing coil I4.

If with spring blade 'I in this position the aircraft is outside a gun-laying area, no signals are received or accepted by selector a from either gun-laying stations or early-warning stations. Further, the valve in the D. C. amplifier h is not able to conduct because of the cutoii bias applied to its control grid. This period exists for two seconds, being terminated when cam 8 releases spring blade 'l to again make contact with Contact I0 and break contact with contacts 3 and I3. plied to the anode of the receiving valve in stage 12", and hence signals from early-warning stations are again received and accepted by selector a" for a period of fourteen seconds. After this fourteen-second period the high-tension supply is disconnected from receiving valve a" and again 1 connected to the receiving valve in stage b.

Thus, this first-described position of the changeover switch is one which permits the several responders to operate singly in a predetermined cyclic order. So long as the aircraft is outside a gun-laying area, it receives sig-nal pulses from early-warning stations for fourteen seconds and then for two seconds it receives or accepts nothing.

If, however, the aircraft enters a gun-laying area during the period when the signals transmitted from early-warning stations are being received, the connection of the high-tension supply to the anode of the receiving valve in sta-ge b at the end of a fourteen-second period allows signals transmitted from a gun-laying station to be received. Also, the valve in the D. C. amplifier h now conducts because the high-tension supply is connected to it and because the repetition frequency of the pulses transmitted from a gun-laying station and translated by superregenerator b' is such as to cause the build-up of a potential across the diode rectierg of suflicient amount to overcome the cutoif bias applied to the control grid of the valve on thermionic amplifier h.

Conduction of this valve causes energizing coil I4 to actuate and move the change-over switch to its second position in which the double-break single-pole switch elements i, 3 and 4 are closed and switch elements 2 and 5 are opened. Closure of switch element 3 permits the l2-volts supply E to be applied to the hold-on coil I2 by way of spring blade II (the contacts IIa and lib of which are now closed). This coil aids coil I4 in maintaining switches I, 3 and 4 closed.

This operation is more or less instantaneous and exists for a period of two seconds. At the end of this period spring blade 1 makes contact The high-tension supply is now reapf with contact IE and breaks contact with contacts 9 and I3. Coil I4 is no longer energized because the high-tension supply is disconnected from the D. C. ampliiier h, but, since switch 3 is closed and coil I2 is energized, the double-break single-pole switches I, 3 and 4 remain closed. Signals from a gun-laying station continue to be received for a further period of thirteen seconds.

At this instant contacts I la and I Ib are broken, coil I2 is no longer energized since the 12-volts supply E is no longer applied to it and thus the change-over switch is returned from its second position back to its rst position in which doublebreak single-pole switch elements I, 3 and 4 are opened and double-break single-pole switch elements 2 and 5 are closed as shown in Fig. 3. Signals may now be received from early-warning stations. After one-half of a second spring blade 'I agains makes contact with contacts 9 and I3 to initiate the normal two-second operation of the responder means :r which is responsive to gun-laying stations. If during this period the aircraft is still in a gun-laying area, signals are received by the valve in stage b', the change-over switch is restored to its second position in the manner already described, and reception of signals from the gun-laying station is sustained for a further thirteen-second period as before.

If, however, the aircraft has left a gun-laying area, no signals are accepted during the period when spring blade 7 is in contact with contacts 9 and 3, and when, at the end of this period, these contacts are broken, the apparatus reverts to the first-mentioned operating condition for receiving signals from early-warning stations.

If the aircraft enters a gun-laying area while the change-over switch is in its second position and connecting the positive terminal of the hightension supply to the anode of the receiving valve in stage b', signals from the gun-laying station are immediately received, and continue to be received until contacts I Ia and I Ib are subsequently broken, the mode of operation being exactly as described above.

It will thus be seen that while the aircraft is outside the area of a gun-laying station, the change-over switch is in its iirst operating position, permitting each of the thermionic-valve systems comprising the responder means :c and y to operate singly in turn for the periods of two and fourteen seconds respectively assigned thereto by the cyclically operating switching means consisting of the cam-controlled spring blade I and contacts 9 and it. With the change-over switch in this position, cam 8 and contacts I and I 3 constitute automatic means for establishing at regular intervals a condition favorable to movement of the change-over switch from its first to its other operating position. The regular intervals referred to correspond to the operating periods cyclically assigned to responder x by cam 8 and contacts 'I and 9.

When however, the aircraft enters the area of a gun-laying station and it is accordingly desired that substantially uninterrupted operation of the specific system :c responsive to such station should take place, the reception by the responder means :c of gun-laying station signals during its twosecond cyclic operative period is characterized by the conduction of the D. C. amplifier h. Coil I4 comprises electromagnetic actuating means, actuated by occurrence during that two-second period of a signal output from responder :r which is present only when substantially uninterrupted operation of that responder is desired, for moving the change-over switch. This effects movement of the change-over switch to its opposite or second operating position and its being held in this position by means of coil I2 until released by opening of contacts H, llajust'fbefore the system is again due to bevput `into operation for its cyclic two-second period .by the cyclically operated spring blade 1. If the aircraft is still within a gun-laying station area a repetition of events takes place whereby the system .ris operated continuously except for alshort ,interruption at the end of each cycle of the arrangement.

An indication as to .whether an` aircraft is in a gun-laying arealornot is` given to the pilot by means of lamps I `and I6 which may be diier ently colored. When in a gun-laying area doublebreak single-pole switchelement `l is closed and the :l2-volts supply E is applied to lamp l5. When outside a gun-layingarea, switch element 4 is open and switch element 5 is closed, thereby connecting the 12fvolt's supply E to lamp I6.

In arrangements comprising two or more responder systems as above described certain didiculties may be found to arise during period of change-over from one thermionic-valve system to another, that is to say, when the high-tension supply is disconnected from one valve system and connected to another.

The first diflicultyarises from the fact that the receiving valve and transmitting valve of each responder system` are usually each` provided with an automatic grid-biasing: arrangement comprising a resistance in parallel with a condenser in their respective cathode leads. Consequently,

when after one such system has been operating,

the high-tension` supplyto it is disconnected due to movement of the spring. blade l, the condenser forming part of the grid-biasing means discharges and the potentialof the cathode of the valve becomes nearly equal to earth potential. When the high-tension supply to' this particular system is switched on again after a period during which the other responder system has been operating, the negative bias potential applied to the receiving valve and the transmitting valve .in the rstmentioned system is small since their cathodes are nearly at earth potential, and it is. usually so small as to allow'self-oscillation to occur in each control-grid cathode circuit thereby causing unwanted transmission. This state of aiars continues until the cathode potentials rise to their normal operating values.

A second diiculty may arise because a D. C. connection is usually made to the control grid of the transmitting valve in the units Ic and k' in each responderirom the cathode or anode of the valve in the amplifier stage e (Fig. 2) which is common to bothmeans. When a signal pulse is received by anoperating responder, the potential of the anode or cathode of the common amplier valve in stage e rises. Hence not. only does the potential of the controll grid of the transmitting valve in the operating means rise positively, but so does the potential of the control .grid of the transmitting valve inl the nonoperating means. In the case of this latter valve. .its anode potential is zero, its control-grid potential is positive and its cathode potentialis nearly that of earth. Consequently, the control grid and cathode of this transmitting valve may operate as a diode valve, the control grid takingcurrent. It will thus be seen that `a transmitting valve in a nonoperating means maythus add` an extra load to the common amplifier valve, thereby reducingthe driving power applied tothe transmitting valve in the operating responder system. This would cause a reduction in the amplitude of the pulse transmitted from the operating responder. Furthermore, the width oi the pulse may be aiected since the current through the pulse-widening circuit will then include a component due to grid current in the transmitting valve in the nonopel'- ating responder system.

Fig. 4 shows an arrangement in accordance with the invention by which the above outlined diiculties may beavoided. In this ligure, which shows two responder systems controlled by switching means similar to those of Figs. 2 and 3, the iirst responder system includes a receiver stage b' comprising a superregeneratively operated valve 2li having a parallel tuned resonant circuit a connected between its anode and control grid with a tap on the inductance coil of such tuned circuit connected by way of contact 9 and spring blade l to the positive terminal of the high-tension supply source S. The cathode of the valve 29 is connected by way of an automatic grid-biasing arrangement comprising resistance 22 and parallel condenser 23 to the negative terminal of the supply source S.

The transmitting oscillator valve 2 l of the rst responder system is also arranged with the same tuned circuit a connected between its anode and control grid while its cathode is likewise connected to the negative terminal of the high-tension supply S by way of a separate grid-biasing network of resistance 26' and parallel condenser 2l. This oscillator valve 2| is normally held inoperative by virtue of the value of negative grid bias ap plied thereto.

The second responder system is composed of substantially identical components and as these have similar reference numerals double primed, they will not be further described. The tap `on the inductance coil a" is connected in this instance by way of ContactJ Iii and spring blade l to the positive terminal of the source S whereby each system may be operated alternately by appropriate movement of the spring blade 'l as already described in connection with Fig. 3.

The amplified received signal pulses in tuned circuit a of Fig. 4 are fed by way of condenser 30' to a detector circuit, such as that of d', Fig. 2, and the rectified output of the latter is then applied to the input circuit of an amplifier Valve 29 constituting the equivalent of the stage e, Fig. 2. The circuit is arranged in such manner that a received signal pulse causes a rise in potential at either the anode, or preferably as shown, the cathode of the Valve 29, and this rise is applied as a positive pulse to the control grid of the oscillator Valve 2 l by way of pulse-widening circuit f', consisting of a parallel resistance-condenser network of suitable values. The application of this positive pulse to the control grid of the oscillator valve 2 l causes the latter to burst into oscillation at the resonance frequency of the tuned circuit a whereby a response signal is radiated in reply to the incoming pulse signal which initiated it. The Value of the condenser of the pulsewidening circuit f may be varied automatically by suitable driving means as already described in connection with Figs. 2 and 3 for the purpose of eecting a predetermined alteration in the width of the response signals to provide a coded reply signal in the manner more fully del scribed in a copending application of Maurice K. Taylor and Frederic C. Williams, nled November 5, 1945, Serial No. 29,284/45, entitled improvements relating to Therrnonic valve systems, and

i i assigned to the same assignee as the present application.

The amplified received signal pulses in tuned circuit a of the second responder system are similarly applied by way of a detector stage d", to the amplier valve 29, the latter being made common to both systems for the purpose of economy in both cost, weight and power supply. The output potential of such valve, at either its anode or. as shown, its cathode is then applied by way of the pulse-widening circuit f to the control grid of the oscillator valve 2l of this second responder system.

The manner of operation of the arrangement so i'ar described has already been adequately dealt with and difficulty may arise in practice as outlined. For example, if the responder system comprising valves and 2i is operating by virtue of spring blade 'i being in engagement with contact it?, the cathode potential of both valves 2G and 2l falls to that of the earthed negative high-tension supply terminal. While this is so, the positive pulses supplied from the ampliiier valve 29 may raise the control grid of the valve 2| to such a potential that the control grid and cathode of this valve operate as a diode thus adding an extra and wasteful load upon the valve 29. When the spring blade 'l is operated to transfer high-tension supply to the valves and 2i' by way of Contact 9, the zero grid bias existing initially on each valve may give rise to self-oscillating conditions until the condensers 23 and 2l become charged in the normal manner.

To obviate these difculties, the cathode of valve 28 is connected by way of resistance 24 to the common high-tension supply lead to valves 2i?" and 2l while the cathode of valve 2l is likewise connected to the same high-tension supply lead by way of resistance 23. Similarly the cathode of valves 2li and 2i are each connected by way of resistances 2li" and 23 to the common high-tension supply lead to valves 2li and 2l.

In the operation of this, now modified, arrangement, when the spring blade 'l is in such a position as to connect the positive terminal of the high-tension supply S to the anodes of the rst receiving and transmitting valves 2E' and 2l the cathodes of the second receiving and transmitting valves 2li and 2l are maintained at a positive potential (with respect to their related control grids) because of the connections thereto from the high-tension supply to the rst valve system. Also when the spring blade l is in such a position as to connect the positive terminal of the high-tension supply to the anodes of the second receiving and transmitting valves 2U and 2|, the cathodes of the iirst receiving and transmitting valves 20 and 2l are likewise maintained at a positive potential (with respect to their related control grids).

By suitable choice of value for the resistances 25', '28 and 2d, 28" the potentials of the cathodes of each receiving valve and transmitting valve in any nonoperating system may be arranged to be greater than that of their related control grids even during the period of application of a positive pulse from the amplier valve 29 whereby such control grids and cathodes do not act as diode valves.

The arrangement may clearly be applied to three or more valve systems, each means being arranged to operate in turn. Connections are 1'12 made from the high-tension'su'pply line of each system by way of resistances to vthecath'odes of the receiving and transmitting valves in each of the other systems.

Thus it .will be seen that during its period of nonoperation, the cathode of each valve is held positive and that when the high-tension supply tc such valve is switched on self -oscillation thereof is prevented.

Provided the switching-off of one thermionicvalve system and the switching-on of another system is effected substantiallyinstantaneously, the arrangements so far described have been found satisfactory. If however, as frequently happens in practice, the switching means is such that there is a small time delay of the order of say one or two milliseconds between the switching-oir of one system andthe switching-on of another system a further' dilculty may loccur since, during this delay period the cathode potentials of the system which'is about to become operative may fall from the values at which they have been maintained while nonoperative and self-oscillation may again occur.

To overcome this diiculty, the cathode of each of the valves is connected by way of a suitable capacitance to its own high-tension supply. Referring again to Fig. 4, a condenser 25 is connected between the cathode ofvalve 20 and its high-tension supply lea'dvvhilev a condenser 29 is connected between the cathode of valve 2 l and the same high-tension supplyflead Similarly, condensers 25" and 29". are connected respectively between thecathodesof valves 20 and El and the high-tensionl supply lead thereto.

The operation with this modification is as already described With the following additional diierences. During the 'period between switching oir, say, the pair of valves 20" and 2l and switching on the other pair of valves 2li and 2 I the potentials of the cathodes'of the second pair of valves will fall from their positive values, the condenser of each gridfbiasing means discharging to earth by Way of its parallel resistance. Although the time period involved may be small, it may be suicient to allow such a potential fall that self-oscillation will take place in the valves owing to an insufficient grid-bias potential at the moment when anode voltage is applied were it not for the condensers ,25" and 29' which are connected between the high-tension supply line and the cathodes of the tWovalves. The capacity of these condensers is so chosen that the cathode potential of each valve rises with that of the anode, thereby charging momentarily the condenser of each grid-biasing means-to an excessive potential. These potentials fall to the operating value as the condensers discharge to earth.

Similarly self-oscillation. of the other pair of valves 20 and.2l at the" instant of applying the high-tension supply thereto is prevented by the similarly connected condensers 25" and 29".

This feature of thel invention may likewise be applied to three "o r more systems, each system being arranged to operate in turn, the cathode of each receiving valve and each transmitting valve being returned to its own high-tension supply line by way of a condenser.

Thus it will be seen that during the period of nonoperation, the cathode of a valve is held positive and then when -the.high-tension.supply to a valve is switched on the cathode potential instantaneously rises with that of the anode. Thus self-oscillation of any valve'is prevented.

Although the invention' has beenl described with reference to responder systems as embodied in an aircraft for the purpose ofindicating its nature to an interrogating ground station, it is also applicable to any other thermionic-valve systems which are arranged to operate singly in a predetermined order.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modications may be made therein Without departing from the invention, and it is, therefore, aimed to cover all such changes and modications as fall Within the true spirit and scope of the invention.

What is claimed is:

1. A thermionic-valve system comprising: a plurality of selectably operated thermionic-valve oscillatory systems each including at least one oscillator valve having an input circuit therefor; a high-voltage energizing source for said oscillatory systems; self-bias means in each of said input circuits for developing a self-bias potential for the oscillator valve associated therewith when the oscillatory system including said associated oscillator valve is selectably operated; and a control system for temporarily applying from said source a control potential to the self-bias means of the oscillator valve in each nonoperating oscillatory system to prevent self-oscillation immediately upon selection of a nonoperating oscillatory system for operation.

2. A thermionic-valve system comprising: a plurality of selectably operated thermionic-valve oscillatory systems each including at least one oscillator valve having an input circuit therefor; self-bias means in each of said input circuits for developing a self-bias potential for the oscillator valve associated therewith when the oscillatory system including said associated oscillator valve is selectably operated; a control system for applying, when any selected one of said oscillatory systems is operating, a control potential to the self-bias means of the oscillator valve in each nonoperating oscillatory system to prevent selfoscillation immediately upon selection of a nonoperating oscillatory system for operation; and means, responsive to the selection of said lastmentioned system for operation, for removing said control potential from the self-bias means of the oscillator valve thereof.

3. A thermionic-valve system comprising: a plurality of selectably operated thermionic-valve oscillatory systems each including at least one oscillator valve having an input circuit therefor; self-bias means including a cathode resistor in each of said input circuits for developing a selfbias potential for the oscillator valve associated therewith when the oscillatory system including said associated oscillator valve is selectably operated; a control system for applying, when any selected one of said oscillatory systems is operating, a control potential to the cathode resistor of the oscillator valve in each nonoperating oscillatory system to prevent self-oscillation immediately upon selection of a nonoperating oscillatory system for operation; and means, responsive to the selection of said last-mentioned system for operation, for removing said control potential from the cathode resistor of the oscillator valve thereof.

4. A thermionic-valve system comprising: a plurality of selectably operated thermionic-valve oscillatory systems each including at least one oscillator valve having a cathode and including an input circuit coupled thereto; self-bias means including a cathode resistor in each of said input circuits for developing a positive Selfrbias potential at the cathode of the oscillator` valve associated therewith when the oscillatory system including said associated oscillator valve is `selectably operated; a control system for applying, when any selected one of said oscillatory systems is operating, a positive control potential to the cathode of the oscillator Valve in each nonoperating oscillatory system to prevent self-oscillation immediately upon selection of a nonoperating oscillatory system for operation; and means, responsive to the selection of said last-mentioned system for operation, for removing said positive control potential from the cathode of the oscillator valve thereof.

5. A thermionic-valve system comprising; a

plurality of selectably operated thermionic-valve' oscillatory systems each including at least one oscillator valve having an input circuit therefor; a source of high-voltage energizing potential for said oscillator valves; self-bias means in each of said input circuits for developing a self-bias potential for the oscillator valve associated there- With when the oscillatory system including said associated oscillator valve is selectably operated by the application of said energizing potential thereto; a control system for deriving from any selected one of said oscillatory systems during operation thereof a control potential and for applying said control potential to the self-bias means of the oscillator valve in each nonoperating cscillatory system to prevent self-oscillation immediately upon selection of a nonoperating oscillatory system for operation; and means, responsive to the selection of said last-mentioned system for operation, for removing said control potential from the self-bias means of the oscillator valve thereof.

6. A thermionic-valve system comprising: a plurality of selectably operated thermionic-val've oscillatory systems each including at least one oscillator valve having a cathode and including an input circuit coupled thereto; a source of high-voltage energizing potential forsaid oscillator valves; self-bias means including a cathode resistor in each of said input circuits for developing a positive self-bias potential at the cathode of the oscillator valve associated therewith when the oscillatory system including said associated oscillator valve is selectably operated by the application of said energizing potential thereto; a control system including said resistors individual` to each of said oscillator valves for deriving from any selected one of said oscillatory systems during operation thereof a positive control potential and for applying said derived potential to the cathode of the oscillator valve in each nonoperating oscillatory system to prevent self-oscillation immediately upon selection of a nonoperating oscillatory system for operation; and means, responsive to the selection of said last-mentioned system for operation, for removing said positive control potential from the cathode of the oscillator valve thereof.

7. A thermionic-valve system in accordance with claim 6, in which each of said plurality of thermionic-valve oscillatory systems includes a plurality of oscillator valves.

8. A thermionic-valve system comprising: a plurality of selectably operated thermionic-valve oscillatory systems each including at least one oscillator valve having a cathode resistor and including an input circuit coupled thereto; a source of high-voltage energizing potential for said oscillator valves; self-bias means including a cathode resistor in each of said input circuits for developing a positive self-bias potential at the cathode of the oscillator valve associated therewith when the oscillatory system including said associated oscillator valve is selectably operated by the application of said energizing potential thereto; a control system including said resistors individual to each of said oscillator valves for deriving from any selected one of said oscillatory systems during operation thereof a rst positive control potential and for applying said derived potential to the cathode of the oscillator valve in each nonoperating oscillatory system to prevent self-oscillation immediately upon selection of a nonoperating oscillatory system for operation; means, responsive to the selection of said last-mentioned system for operation, for removing said positive control potential from the cathode of the oscillator valve thereof; and means including individual condensers for each of said oscillator valves and responsive to said selection of said last-mentioned oscillatory system for applying to the cathode resistor of each oscillator valve thereof during an immediately subsequent relatively short time interval a second positive control potential effective further to prevent said self-oscillation during said interval.

9. A thermionic-valve system in accordance with claim 8, in which each of said plurality of thermionic-valve oscillatory systems includes a plurality of oscillator valves.

10. A thermionic-valve system comprising: a plurality of selectably operated thermionic-valve oscillatory systems each including at least one oscillator valve having an input circuit therefor; a high-voltage energizing source for said oscillatory systems; self-bias means in each of said input circuits for developing a self-bias potential for the oscillator valve associated therewith when the oscillatory system including said associated oscillator valve is selectably operated; and a control system responsive to the selection of any nonoperating oscillatory system for applying from said source to the self-bias means of each oscillator valve thereof during an immediately subsequent relatively short time interval a control potential effective to prevent self-oscillation of said last-mentioned system during said interval.

11. A thermionic-valve system comprising: a plurality of selectably operated thermionic-valve oscillatory systems each including at least one os- 16 Y cillator valve having an input circuit therefor; self-bias means in each of said input circuits for developing a self-bias potential for the oscillator valve associated therewith when the oscillatory system including said associated oscillator valve is selectably operated; a control system for applying, when any selected one of said oscillatory systems is operating, a control potential to the self-bias means of the oscillator valve in each nonoperating oscillatory system to prevent selfoscillation immediately upon selection of a nonoperating oscillatory system for operation; and a control arrangement, for selectably operating each of said plurality of oscillatory systems singly in predetermined cyclic order. including switching means responsive to the selection of a nonoperating oscillatory system for operation for removing said control -potential from the self-bias means of the oscillator valve thereof.

12. A thermionic-valve system comprising: a plurality of selectably operated thermionic-valve oscillatory systems each including at least one oscillator valve having an input circuit therefor; self-bias means in each of said input circuits for developing a self-bias potential for the oscillator valve associated therewith when the oscillatory system including said associated oscillator valve is selectably operated; a control system for applying, when any selected one of said oscillatory systems is operating, a control potential to the self-bias means of the oscillator valve in each nonoperating oscillatory system to prevent selfoscillation immediately upon selection of a nonoperating oscillatory system for operation; and a control arrangement, for permitting each of said plurality of oscillatory systems to operate singly in predetermined cyclic order or for permitting the substantially uninterrupted operation of only a specic one of said oscillatory systems, including switching means responsive to the selection of a nonoperating oscillatory system for operation for removing said control potential from the self-bias means of the oscillator valve thereof.

MAURICE K. TAYLOR. FREDERIC C. WILLIAMS.

REFERENCES CITED UNITED STATES PATENTS Name Date Lowell Mar. 22, 1938 Number 

